Application of Distance-Based Clustering in the Evaluation of Fluvial Composite Sand-Body: A Case Study of the Minghua Town Formation in the North Area of Q Oilfield

Fluvial facies is controlled by high-frequency base-level changes and frequent migration, evolution, erosion, and superimposition, forming structurally complex and strongly heterogeneous reservoirs. This leads to poor efficiency of oil recovery and dispersed remaining oil in fluvial facies oil fields, resulting in a much lower recovery rate compared to marine sandstone reservoirs. Based on the theory of Fluvial reservoir configuration, this paper proposes a set of quality characteristic parameters for complex sand bodies, which describe the characteristics of the reservoir architecture including the parameters related to structural features, geometric features, physical properties, and heterogeneity characteristics. The paper also proposes that the scale of the reservoir is a necessary condition for forming high-quality reservoirs, and the reservoir structure is the key factor controlling reservoir quality. Using the guidance of the complex sand body quality characteristic parameter and the reservoir quality control mechanism, an improved distance clustering method based on principal component analysis is used to establish a quality evaluation process for complex sand bodies.Taking the R23 unit of the lower section of the Minghuazhen Formation in the Qinhuangdao 32–6 oil field as an example, the optimal quality of complex sand bodies is evaluated. The best type of complex sand body has a larger sand body thickness, which is a superimposed or closely stacked complex point-bar sand body. The complex sand body has a simple sand body structure, good connectivity, and high initial and cumulative production, with good development effect. However, the bottom of the sand body is generally quickly flooded with water, and remaining oil is mainly distributed in the upper part of the sand body. The quality of the second and third types of complex sand bodies is moderate, and the exploitation effect is poorer than that of the first type of reservoir. They can be used as targets for adjusting the potential of production in the later stage of oil field development.